Like autos and airplanes, reuire citizens post cash bond of $40,000 or have gun liability insurance to own a firearm and purchase ammunition. Manage it just like car insurance.
The NRA could offer/partner with a large insurance company to insure members. No gun could be purchased or ammo bought/sold without proof of insurance.
The free market would offer discounts on premiums for gun training, lockable gun storage. Those with large arsenals could possibly qualify for a multi-gun discount.